The middle Ordocivian Lashizhong Formation in Zhuozishan area contains mainly dark-gray shale, grayish-green sandstone, siltstone and taupe-gray conglomerate, which could be divided into three members. Based on an analysis of the lithologic character, sedimentary structure, palaeobiologic fossils and geochemical indicators, it is believed that the sedimentary environment of Lashizhong Formation is a deep-water slope to basin margin environment. The results of sedimentary facies analysis show that the slope facies and basin margin facies are main depositional facies in the study area, which can be further divided into two subfacies: the upper slope and lower of slope sediments, and three microfacies: proximal channel, distal channel and levee sediments. The litho-section on the whole covers a complete sedimentation cycle of marine transgression and marine ingression.